Design and Fabrication of Modular Wearable Biosensors through the Development of Anthropomorphic Materials

<p dir="ltr">Wearables are a collection of body worn devices that offer unique, portable data capabilities for a plethora of applications in healthcare, sports, prosthetics, and robotics. Body worn devices demand integrated electronics that bend, flex, and stretch in soft, docile contusions to match the complex movements of the human body. This thesis represents the journey from concept to implementation of soft and self-healing materials into body-worn anthropomorphic devices that capture body movements, electrophysiological activity, and act as human machine interfaces through sensors that measure tactile interactions with the environment.</p><p dir="ltr">The first body of work observes the evolution of a Silver-Thiol self-healing matrix into a variety of composites targeting different electromechanical scenarios. MWCNT and graphene-based composites were able to generate high organic conductivities of 2×10^-2 S/m with complementary hardening on mechanical stiffness. PZT composites demonstrated the ability to directly improve on electric charge carrying capacity at low concentrations, increasing the relative dielectric constant threefold to 6.23. Silica particles were observed to allow for the tailoring of mechanical stiffnesses without causing significant attrition to electrical properties, increasing the Young’s Modulus up to 503.3 kPa with 20% nanofiller. Irrespective of the neat or composited matrices, all samples were observed to chemically bond across their interfaces, demonstrating a seamless connection via their intrinsic healing mechanism.</p><p dir="ltr">The second body of work observes the application of the self-healing elastomer and its composites into functional devices. Proprioceptive sensing devices were observed to easily attach to the body and reflect changes in joint movements and skin extension. These devices were connected with high-weight composites acting as electronic interconnects and could observe a healing efficiency of 92% with 2 hours of interfacial contact. Electrophysiological monitoring was conducted with high-weight MWCNT composites acting as dry, self-healing electrodes that demonstrated skin-like mechanical behaviour and are electrically stable for over 21 days of continuous monitoring. Comparisons to pristine AgCl electrodes demonstrate weaker, but markedly similar EMG responses under rapid and loaded conditions. Extended ECG testing shows significantly more robust results against AgCl electrodes over a 14-day period, with damaged electrodes recovering to 98.7% of their original performance after 2 hours of healing. Integration into a gesture recognition system yields 5 independent gestures for a prosthetic hand.</p><p dir="ltr">Applications of these technologies trickle into the design of a multi-modal normal pressure, surface shear, temperature, and texture tactile sensor. The tactile sensor was empirically investigated for its ability to independently detect the tactile modes in a repeatable unit for future tessellation. Normal pressure measurements yield a gauge factor and sensitivity of 8.743 and 0.01 kPa^-1 , respectively, through a dynamic range of 176,000:1 and bandwidth of 8 Hz. These properties were maintained through shear loadings, achieving a gauge factor and sensitivity of 0.8544 and 0.006 kPa^-1, respectively. Thermal detection was independently detectable and sees a maximum sensitivity of 1.71×10^-3 ℃^-1. The novelty in this design is its easy networking into an array architecture as the underlying design is founded in a standard matrix style capacitance sensor.</p><p dir="ltr">The primary contributions of this thesis lie in 3 main categories. The first is in the design, fabrication, and characterisation of a series of room-temperature, self-healing nanocomposites that form the foundations to an anthropomorphic wearable system. The second, is the demonstration of such wearable system in the form of human machine interfaces, including proprioceptive and electrophysiological monitoring techniques. The last significant contribution is the design and development of a multi-modal tactile sensor capable of tessellating pressure, shear, temperature, and texture monitoring over a minimal demand in electrical hardware, which, at the time of writing, appears to be one of the first designs to achieve this.</p><p dir="ltr"><br></p>